Spindle motor

Abstract

A spindle motor includes a shaft, a hub assembly unit rotatable relative to the shaft, an upper bearing structure and a lower bearing structure both interposed between the shaft and the hub assembly unit, and a stator disposed between the upper and lower bearing structures. The stator, the hub assembly unit, and the upper and lower bearing structures are attached to a specific side of the shaft. The hub assembly unit has an aluminum-made hub and an iron-made yoke, both of which are joined together through a pair of fixing portions. One fixing portion has a relatively strong fitting force, whereas the other fixing portion has a relatively weak fitting force.

What is claimed is: 
     
       1. A spindle motor comprising: a shaft;   a hub assembly unit rotatable relative to said shaft;   an upper bearing structure and a lower bearing structure both interposed between said shaft and said hub assembly unit; and a stator disposed between said upper bearing structure and said lower bearing structure, wherein said hub assembly unit and said upper bearing structure constitute a unit assembly, said lower bearing structure being formed of a bearing member along with an annular member fitted with an outer ring of said bearing member, said upper bearing structure being formed of a bearing member, said lower bearing structure, said stator and said unit assembly being mounted on the shaft in this order, all from the same direction of said shaft, said annular member of said lower bearing structure supporting one end of said hub assembly unit, and said bearing member of said upper bearing structure supporting the other end of said hub assembly unit.     
     
     
       2. A spindle motor according to claim 1, wherein said shaft has a large-diameter portion with a relatively large diameter, a small-diameter portion with a relatively small diameter, and a medium-diameter portion with a diameter intermediate between said large-diameter portion and said small-diameter portion, said lower bearing structure being attached to said large-diameter portion, said stator being attached to said medium-diameter portion, said upper bearing structure being attached to said small-diameter portion. 
     
     
       3. A spindle motor according to claim 2, wherein a first contact portion is provided at one end of said large-diameter portion and a second contact portion is provided at one end of said medium-diameter portion, whereby said lower bearing structure comes into contact with said first contact portion and is thereby positioned with respect to said large-diameter portion and said stator comes into contact with said second contact portion and is thereby positioned with respect to said medium-diameter portion. 
     
     
       4. A spindle motor according to claim 1, wherein labyrinth seal means is provided outside said upper bearing structure. 
     
     
       5. A spindle motor according to claim 1, wherein said shaft is provided integrally with a bracket which attaches to a frame of a disk driving device. 
     
     
       6. A spindle motor comprising: a hub with which a recording disk fits;   a yoke disposed inside said hub; and   a rotor magnet disposed inside said yoke;   wherein said hub and said yoke are formed of materials having different coefficients of thermal expansion;   wherein said hub is secured to said yoke through two or more annular fixing portions, a specific fixing portion of the two or more fixing portions having a relatively strong fitting force, the remaining fixing portions having a relatively weak fitting force; and   wherein when temperature varies greatly, said hub and said yoke remain fixed in the specific fixing portion, slippage being produced between said hub and said yoke in the remaining fixing portions.   
     
     
       7. A spindle motor according to claim 6, wherein said hub is secured to said yoke through two annular fixing portions, one fixing portion having a relatively strong fitting force, the other fixing portion having a relatively weak fitting force; and wherein when temperature varies greatly, said hub and said yoke remain fixed in the one fixing portion, slippage being produced between said hub and said yoke in the other fixing portion.   
     
     
       8. A spindle motor according to claim 7, wherein an area of the one fixing portion where said hub is in contact with said yoke is relatively wide, an area of the other fixing portion where said hub is in contact with said yoke being relatively small. 
     
     
       9. A spindle motor according to claim 7, wherein a first annular projection extending toward said yoke is provided on an inner peripheral surface of said hub in the one fixing portion, a second annular projection extending toward said yoke being provided on the inner peripheral surface of said hub in the other fixing portion, said first annular projection extending a little more toward said yoke than said second annular projection. 
     
     
       10. A spindle motor according to claim 7, wherein a first annular projection extending toward said hub is provided on an outer peripheral surface of said yoke in the one fixing portion, a second annular projection extending toward said yoke being provided on the inner peripheral surface of said hub in the outer fixing portion, said first annular projection extending a little more toward said yoke than said second annular projection. 
     
     
       11. A spindle motor according to claim 6, wherein said hub is formed of aluminum or aluminum alloy, said yoke being formed of iron.